There are assault weapons, but you can’t easily own them legally. They would be NFA weapons and have to have been made and registered before 1986. That leads to exorbitant prices on the few put up for sale. You might be able to find an 60-80s M16. There are some WII and Korean War weapons out there. They all have 5 figure price tags though. http://www.dndguns.com/colt_xm16e1.htm